Coaxial cable transmission networks for distributing cable television services are in wide use in many cities and towns, and provide excellent services for distributing television signals to television sets of subscribers on the network. Such cable television distribution systems are based on a coaxial wire cable, having a single central conductive core, and a woven sheath of wire or other form of conductive sheath, insulated from the core. Such coaxial cable is capable of transmitting great volumes of information at high speed, and with very little interference. In the past such cable systems have been used for one way transmission of television signals from the head end signal source to the consumers television sets. Forward amplifiers are provided at intervals to maintain signal strength, which would otherwise become attenuated, due to the length of the cable system. Such forward amplifiers usually incorporated signal strength equalizers and attenuators for equalizing the signal strengths across the frequency band of the signals. In other cases equalizers were provided separate from the forward amplifiers
The existence of wide spread cable television signal networks has lead to the development of their use as a means of connecting consumers to the Internet system. The coaxial cable systems, with forward signal amplifiers and equalizers located along the cables at spaced intervals, and with their substantial freedom from interference, lend themselves particularly well to the rapid transmission of high volume signals such as are generated by the Internet system. Consequently consumers are increasingly looking to the coaxial cable television networks as a means of connecting their computers to the Internet, so as to avoid the difficulties of connections via the telephone wire systems.
One of the problems encountered in using coaxial cable networks for distribution of Internet signals is that Internet signals travel in two directions, both to and from the consumer. This is unlike television signals, which travel in the forward direction, from the supplier to the consumer. To carry Internet signals, the coaxial cables are required to carry signals in both directions simultaneously. The consumer will be receiving signals from an Internet service provider (ISP), and will be generating return signals, generated from his or her computer, back onto to the Internet. In theory the coaxial cable networks are ideally suited to this type of two-way transmission. In practice however, there are problems which arise from the original design of such cable systems. Since the coaxial cable networks are relatively long, the forward signals on the networks gradually become attenuated and decrease in strength as they pass along the length of the cable. It is well known that signal attenuation is greatest in the high frequency end of the bandwidth and progressively decrease down to the low end
of frequency. The end result is a signal which is unbalanced, and the condition is know as “signal slope” or “slope loss”. In the case of television forward signals this problem is overcome, as mentioned above, by the use of forward signal equalizers located in the coaxial cables at spaced intervals. These forward signal equalizers together with the usual forward signal amplifiers, ensure that all subscribers on any particular cable network will receive fully balanced equalized signals of adequate strength so that in spite of the considerable length of any one particular cable, and the number of consumers tapping in to the cable, the forward signals will all be substantially of the same balanced signals of adequate signal strength to all households on that cable network.
Such forward signal amplifiers and equalizers are capable only of amplifying the forward signals fed into the coaxial cable from the head end and equalizing them across the forward signal frequency band but cannot amplify or equalize return signals, passing in the opposite direction.
When it is attempted to adapt the coaxial cable system for two-way transmission of Internet signals, the return Internet signals are unable to pass through the forward amplifiers and equalizers already incorporated in the coaxial network. Return signal amplifiers have been used to amplify the return Internet signals. These return signal amplifiers are located alongside the forward amplifiers on the coaxial cable network and pass the return Internet signals around the forward amplifiers, and increase the return Internet signal strength. In this way, the return signals bypass the forward amplifiers, and at the same time their signal strength is maintained at the desired level so that it can be fed back to the Internet server. Other communication may require the sending of reverse signals along the cable, such signals including eg. metering box and telephone signals.
The problem of signal strength is aggravated by the attenuation of signal strength. As mentioned above attenuation varies across the band width, and is greater in the higher range of frequencies, and is lower in the lower range of frequencies. The forward equalizers in use on cable systems are already designed to overcome these problems, and equalize the signal strength over the entire frequency band of the forward television signals. However, the adaptation of an existing cable network to accept two-way transmission of signals such as Internet signals, requires both that the return amplifiers, and also suitable equalizers, be installed on the already existing cable network, and further that the existing forward amplifiers with equalizers shall be modified so as to equalize all signals, both television and Internet, travelling in the forward direction. Alternatively where the existing equalizers can be removed they can be replaced by stand alone equalizers.
Forward equalizers for maintaining level signal strength of the forward signals should be capable of equalizing both the Internet and television signals over the entire frequency range of the signals and to equalize these signals back to a uniform level of signal strength, across the entire range of frequency of both Internet and television signals. However, the signal strength of the signals at any given location on an existing cable network can only be determined by actually measuring the signals at that location. For example when the cable system is modified or new users are added, this signal strength will vary from one location to another. At present, the forward amplifiers and equalizers are produced as standard items, with preset performance. Due to the varying needs at different locations in the system, however, a variety of different forward amplifiers and equalizers are required, which have performance characteristics which vary so as to suit signal strengths from one cable location to another.
Typically, the Internet forward signals are placed within this frequency range of from about 50 to 860 megahertz, ie the usual bandwidth of television signals. Certain other forward signals may also be included in the range. As signal losses occur due to cable attenuation the signals will be unbalanced, by slope losses.
The design and construction of forward signal amplifiers and equalizers for cable systems is dependent upon the fact that the forward amplifiers and equalizers are positioned at spaced locations along any given length of coaxial cable in the system and are located at an elevation upon a cable post, in most cases. Equalizers with standard characteristics will not be equally suitable at each location. In fact, it will be found that before an amplifier or equalizer is installed by the installer, the signal strength at that location in the cable must be tested and an equalizer must be installed having the correct equalizing characteristics for that particular location in the coaxial cable network. These specifications will vary from one location to another along any given length of the coaxial cable.
In normal practice amplifier manufacturers produce a whole range of equalizers having a range of different equalization characteristics. A coaxial line crew carries a large supply of such equipment with them. After testing and checking the signal strength and slope at a particular location, could then select and insert the appropriate amplifier and equalizer having the correct specifications for that location. This method requires a very large investment for supplying an adequate inventory covering a full range of signal characteristics, to each particular line crew. In addition, stocking and transporting such a large inventory covering a wide range of different characteristics, presents a problem of logistics involving a large number of objects with different markings and different characteristics.
A further problem is the fact that the line crew person will be required to climb up the post to reach the coaxial cable. Then the line person must check the signal strength and then come down and select the appropriate equalizer and then climb back up again and insert it. This is a slow and tiresome job.
For all of these reasons, providing an adequate number of equalizers having ranges of different characteristics to meet all conditions and requirements on a given coaxial cable network becomes a logistical nightmare, and a severe financial strain, and causes much undesirable additional labour.
The cable networks carrying television signals are already in existence and the forward amplifiers and equalizers are already in place on posts on those cables. However, as conditions change and as the cable network changes, changes in amplification and equalization may be required.
Adapting the entire cable network by replacing all of the forward equalizers with new equalizers having modified characteristics for equalization, is simply not practical. It also poses the same logistic problem described above.